U.S. Provisional Application No. 61/197,935, filed Oct. 31, 2008, is incorporated herein in its entirety by reference.
In the harvesting of crops it is desired that the grain or seed, hereafter jointly referred to as grain, be separated from other elements or portions of the crop, such as from pod or cob fragments, straw, stalks, and the like.
Agricultural combines typically have employed a rotary threshing or separating system for separating the grain from such other crop elements or portions. In general, a rotary threshing or separating system includes one or more rotors, which can extend axially (front to rear) or transversely within the body of the combine, and which are partially or fully surrounded by a perforated concave. The crop material is threshed and separated by the rotation of the rotor within the concave, and the separated grain, together with some particles, such as chaff, dust, straw, and crop residue collectively referred to as material other than grain (MOG), are discharged through the perforations of the concave so as to fall onto a grain bed or pan, or so as to fall directly onto the cleaning system itself.
Cleaning systems further separate the grain from MOG and typically include a fan directing an air flow stream upwardly and rearwardly through one or more fore to aft reciprocating sieves, typically two, including an upper sieve also referred to as a chaffer, which is more open or coarse, and a lower sieve which is more closed or fine. The air flow stream operates to lift and carry the lighter elements of the MOG towards the rear end of the combine for discharge therefrom. Clean grain, being heavier, and larger pieces of MOG, which are not carried away by the air flow stream, will fall onto the surface of the upper sieve where some or all of the clean grain passes through to the lower, finer sieve. Grain and MOG remaining on the sieve surfaces are physically separated by the reciprocal action of the sieves as the material moves rearwardly therealong. Any grain and/or MOG remaining on the surface of the upper sieve are discharged at the rear of the combine, while grain and/MOG on the lower sieve may be conveyed to an internal tailings system for reprocessing.
The quantity of clean grain and MOG passing through the sieves is typically controllable, in part, by varying the opening size of the sieves. To this end, sieves include rows of fingers, each row supported on an elongate element such as a shaft, together referred to as a slat or louver, which is typically rotatable about a longitudinal axis therethrough for setting a sieve size or gap. A typical sieve includes an adjusting member which contacts each of the slats or louvers. Modern combines use a linkage and/or cable arrangement connected between the adjusting member and one or more manually or automatically movable adjusting elements or adjustors, in the latter instance, which can be moved by an actuator driven by an electrical, fluid, or other controller for moving the linkage or cable arrangement and member and thus changing the angular orientation of the slats and as a result, the opening size.
The adjacent rows of fingers define laterally extending grain passages between confronting surfaces of adjacent rows of fingers. Rotating the longitudinal elements or shafts rotates the rows of fingers through various angular positions, to increase or decrease the opening size of the passages between the adjacent rows. Thus, material passes through the sieve by falling generally vertically through the spaces between the fingers or by entering the passages between the rows and falling through at the angle defined by the angular position of the rows of fingers as the sieve is reciprocated.
Generally, as the rows of fingers are rotated more towards a vertical orientation, the opening size of the passages between the rows is increased to allow more crop material to fall through the sieve through the lateral passages. Also, upward air flow through the sieve will typically be higher as a result of the larger opening size and less restriction. And, because the fingers are more vertical, the grain passages through the sieve are more vertical, so that grain flow through the sieve will be faster and more direct. If the opening size of the passages is too large, a downside is that an increased amount of MOG will be allowed to pass through the sieve. Conversely, as the rows of fingers are rotated more towards a horizontal orientation, the opening size of the passages between the rows is decreased to allow less crop material to fall through the sieve. Because opening size is smaller, upward air flow through the sieve will typically be lower. The grain passages will also be more horizontal, such that grain flow will be longer and less direct, compared to a more vertical orientation. If the opening size of the passages is too small, less MOG is allowed to pass through the sieve, but less clean grain falls through the sieve as well. Therefore, if the sieve passages are opened too much, increased MOG is allowed therethrough, and if the sieve passages are opened too little, less MOG passes therethrough, but grain throughput is reduced.
Often, the sieve setting will be selected for a particular grain variety and other conditions, and the fan speed will be adjusted to achieve an acceptable grain loss level, that is, grain not allowed through the sieve and which is detected as it is discharged past the rear edge of the sieve. In this regard, operators will commonly not be able to achieve optimal grain loss levels of zero or almost zero, and will tolerate greater grain loss than could be attained by adjusting just sieve opening size and fan speed, because minimizing grain loss will often entail opening the upper sieve or chaffer to such an extent that a large amount of MOG will pass therethrough onto the lower sieve, and will be directed by that sieve to the tailings system for reprocessing, sometimes repeatedly.
Many commercially available combine sieves are configured to allow a sufficient range of adjustability of the opening size for accommodating a wide range of crops, including smaller grains such as wheat and rice, and larger grains such as corn, soybeans and other legumes. To have sufficiently large openings for passage of the largest grain sizes, the adjacent slats or louvers must be adequately far apart, and will typically be opened to a relatively upstanding position. In contrast, for the smallest grains, the slats will be positioned more horizontally or closed. As a result, the grain path through the sieve will be longer and less direct, which can negatively affect grain processing and throughput particularly under high yield conditions. A more closed position can also reduce air flow upwardly through the sieve to the region thereabove, which can reduce the cleaning or separating action in that region.
As a proposed solution to the above problems and shortcomings, it is common to utilize different sieves for different crops, a sieve with a larger spacing between adjacent louvers or slats for larger grains, and a sieve with smaller spacing for smaller grains. However, even with multiple sieves available it has been found that it may not always be possible to achieve the best louver spacing or opening size for every crop and crop condition, particularly very large and very small grain sizes.
Ideally while the portion of the flow of crop material including the higher density of grain and MOG is airborne en route to the forward portion of the upper sieve, the flow of air at a significantly higher air flow rate generated by the cleaning fan will be directed therethrough for separating the lighter MOG from the heavier grain such that the lighter MOG will be carried rearwardly over the upper sieve, and the heavier, smaller grain will be allowed to fall onto the upper sieve where it can fall through the spaces between the adjacent fingers of the upper sieve to the lower sieve. Thus, by virtue of the air flow through the airborne flow of crop material, some separation of grain from MOG will occur above the surface of the upper sieve, and some separation will occur on the surface of the upper sieve as a function of the opening size and reciprocation of the upper sieve. That is, under ideal conditions, lighter elements of MOG will be carried by the air flow rearwardly over the upper sieve to be discharged in a desired manner from the combine, heavier elements of MOG will be carried rearwardly by the reciprocating action of the sieves, and grain will fall through the openings of the upper sieve.
When in operation, however, the limited portion of the flow of crop material including the increased density of grain and MOG directed toward the forward portion of the upper sieve having standard spacing between sieve fingers, results in crop material collecting and accumulating on the forward portion of the upper sieve. The accumulation of crop material can build to such an extent as to spill over the forward edge of the upper sieve to the clean grain pan bypassing the lower sieve or into the fan housing. Further, the higher rate air flow stream is unable to pass through the openings of the forward portion of the upper sieve to the extent that the ideal airborne separation above the upper sieve is severely limited or not present at all. As a result the amount of grain cleaned at the forward portion of the upper sieve is severely limited or reduced relative to the ideal situation.
Therefore, what is sought is a sieve for a combine grain cleaning system which overcomes one or more of the problems and shortcomings set forth above.